I had recently encountered the chemical phenomenon commonly known as “salting out”. It’s a captivating process where the addition of salt to a mixture of a liquid and a solid/another liquid induces phase separation in an otherwise miscible solution. My aim was to capture, at a microscopic level, this mesmerizing phenomenon of salt-induced phase separation of two liquids and how they move and interact with each other while separating, and this journey was not without its share of challenges.

I chose household liquids and apparatus for this video project. I tried using distilled water, ethanol, and common salt. But then I found out that ethanol is tricky to salt out and this cannot be achieved by just using common salt. Next, I chose isopropyl alcohol which seemed achievable. Do note that these combinations of liquids are normally miscible but can be separated using processes like distillation, or in this case, salt-induced phase separation. Salting out occurs because the salt disrupts the intermolecular forces between the water and alcohol molecules, reducing their solubility in each other and driving them apart. The addition of dye to the liquids allows for easy visualization of this process, as it helps to distinguish the two phases, so I selected red dye for isopropyl alcohol and blue dye for water. But this again presented issues because the dyes were dissolving in both liquids. So I selected specific markers for this, a normal red permanent marker dissolved in isopropyl alcohol and not in water, and I used a water-based sketching marker to dye the water. I had to dye the water only after dyeing the alcohol and using a dropper to introduce the dye so as to not dye the alcohol blue as well, as it was partially soluble in it. The phase separation of water and alcohol kept the blue from spreading to the alcohol.

I ended up using a small glass vial as a container instead of a glass jar or glass bottle. As the depth of the shot was affecting visual clarity. Focusing proved to be a hurdle, as I worked with a camera lacking a specific focus option, demanding meticulous adjustments in distance. The vial of liquid had to be shaken before each shot, so the initial setup would become worthless if I ended up setting down the vial even 1mm away from its initial spot. This required a lot of takes.

From the clear takes, I saw that there were a huge amount of dust particles that ended up collecting at the alcohol-water interface. These were microscopic, not visible to the naked eye but prominent in the video. I had used distilled water and rinsed the container with alcohol twice, and still, they were present. I realized they might either be contaminants in the salt, or microscopic precipitates forming due to the mixture. In any case, I had to get rid of them, as they were hampering the aesthetics. I tried to edit the video but it was taking a considerable amount of time and also wouldn’t be a true representation. Instead, I tried filtering the mixture three times consecutively and this brought down the level of contaminants to an acceptable level. My next option would have been to distill it, which I’m glad I didn’t have to.

Yet I wasn’t able to capture distinct fluid bubbles initially. I realized lighting was the next hurdle and it indeed became a critical aspect to ensure clear visualization. I initially started out with a lot of diffused light, but the outlines of the bubbles weren’t clear enough. Next, I directly moved to a point source of light in a dark room, and the bubbles became highly shaded and visible. So visible that even the tiniest bubbles could be captured. But this made the video too busy. So I then moved to the slightly diffused single light source, the result of which is shown in the video. I had to include 2 takes, each with slightly changed angle, lighting, and settings, so as to capture the red side and blue side.

I think despite the trials and errors, my persistence paid off, resulting in a captivating representation of the salting-out process in all its microscopic beauty.

Apparatus:

Camera: Canon EOS 1500D
Lens: Canon MP-E 65mm f/2.8 1-5x Macro
Benro MP80 Macro Head

The report is available here: